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final drive pivot bearings


ahirsch

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This is a follow up to a post I did a few weeks ago...

 

 

I noticed oil on rear tire and rim from time to time. When I drain final drive and trans I see clean oil with no metal. I get some play at the 3 and 9 position. None at the 12 and 6. I pulled rubber boot off and a tablespoon of oil was there. Shined a light up the shaft and it is dry. I am assuming the oil is from the rear seal?

 

So my question is do I re torque the pivot bearings?

 

After doing a big search it looks like I need to heat the loctite, loosen lock nut and tighten with the 12 mm allen.

 

Do I do this on both sides? or only the left?

 

Any help is appreciated.

 

Thanks,

 

Andrew

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Well let me tell you a little story...

 

In December about 8 months after a complete tear down for trans rebuild I found my outer race retainer, the one that is a shouldered bolt, non adjustable... about 1/8 threaded out!!! We were coming back from Death Valley Daze 2 up! High speeds all weekend...

 

This was after everything had been solvent cleaned and thread cleared of old Loc Tite. Liberal application of Loc Tite and Torqued with a 3 foot cheater.

 

 

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Covered in many previous threads, but basically:

 

1. Verify whether the play is between the final drive and rear brake rotor, or between the drive/rotor assembly and the swingarm. If the former you've got an internal problem in the FD, if the latter then you can proceed to adjust the swingarm bearings.

 

2. To adjust, remove the left-side pivot pin (the one with the adjusting nut) and clean off the dried Loctite. Note that the locking agent used at the factory is very strong and you will probably need a good amount of heat to release it or you may risk damaging threads. You do not need to touch the right-side pivot pin.

 

3. Adjust the left pivot pin until you feel a very slight drag when moving the final drive up and down, this sets the preload for the tapered roller pivot bearings. BMW's official tightening spec is 7 nm and you should be close to this. Tighten the locknut to 105 nm, making sure that the pivot pin doesn't turn as you tighten it. I use medium-strength (blue) Loctite upon reassembly because the high-strength (red) is such a !@#$% to deal with, but others like to stick with the red, your call.

 

The oil in the boot can come from either the output shaft seal on the transmission or the input shaft seal on the final drive. If it seems dry as you peer up the swingarm then it's probably the FD, but in either case it's nothing to worry about as long as the amount is relatively small.

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Thanks. I am trying to understand everything before proceeding. Couple of questions....

 

 

Can I use a torch. I don't have a heat gun. How do I know when it's hot enough?

 

Do I put lock tite on the pivot pin too?

 

How do I make sure the pivot pin doesn't move when adjusting the lock ring?

 

how/will I be able to move the final drive up and down to test for drag after setting the pivot pin to 7nm?

 

Thanks again.

Andrew

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You can use a torch if you're careful. I would disconnect the rubber boot and maybe place some aluminum foil over it to avoid scorching. Heat until some water sizzles a bit when sprinkled on the area.

 

Yes, Loctite on the pivot pin too.

 

It can be a little tricky to keep the pin from moving. There are special tools to help but what I do is initially torque the locknut with a combination wrench (so I can hold the pivot pin with the Allen wrench) until it is pretty tight and the pivot pin can't move, then touch-up the final torque with a socket and torque wrench. Or you can let the Loctite on the pivot pin set up a bit before you add the locknut.

 

To be clear, BMW's procedure is to set the pivot pin torque to 7 nm and you're done (hence the importance of cleaning the threads to get an accurate reading at such a low torque value.) Since one can't really be sure that 7 nm will equal the correct torque under all circumstances I add the check I described above. If you disconnect the torque arm (the rod that runs from the transmission to the bottom of the final drive) at the final drive then you can move the drive up and down so as to check for proper preload on the bearings.

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I just replaced the OEM needle bearings with JL paralever bushings so I can answer some of your questions.

I used a heat gun and a laser infrared, non-contact thermometer to heat up the inboard pivot pin and lock nut to 250 degrees F. At that temp it came apart without difficulty. I've not used a torch, but have read where others have.

There is loctite on both the pivot pin and lock nut. It is easily removed with nail polish (acetone) and a small brass brush. Make sure you remove the loctite from the threads in the rear drive or the increased drag will throw off any torque reading.

There are several different opinions on what gets loctite (red stuff, #271 at Home Depot). Obviously BMW puts it on both parts. Some advocate just the lock nut or just the pivot pin. If I had the special tool which allows you to hold the pivot pin while torquing the lock nut I would have used it only on the lock nut. Not having that tool I put loctite on the pivot pin, torqued it, allowed it to set up for 3 hours, marked the head with a magic marker, then torqued the lock nut. The mark on the pivot pin allowed me to determine it had not moved--it did not budge.

To test for drag remove the rear bolt on the lower stabilizer bar and move the rear drive up and down. I believe its arc is about 9 degrees.

 

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I think I am ready to go, thanks to your clear and articulate responses. Now the easy part... I just need to acquire the 12mm and 30 mm tools.

 

I am assuming the 12mm allen wrench has to be socket wrench compatible so as to fit on the torque wrench. Is this correct?

 

 

Thanks,

Andrew

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I am assuming the 12mm allen wrench has to be socket wrench compatible so as to fit on the torque wrench. Is this correct?

 

 

Thanks,

Andrew

 

Yes. Got mine at Harbor Freight, very inexpensive; also got the laser infrared temp for about $29

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There is loctite on both the pivot pin and lock nut. It is easily removed with nail polish (acetone) and a small brass brush.

I meant..... nail polish REMOVER (acetone)....

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